Generally, because injectors used in GDI engines for vehicles directly inject fuel into cylinders of the engines, atomization of fuel and atomizing patterns are very important. Such fuel atomization and atomizing patterns are influenced by the shape of a nozzle. Typically, an injector for vehicles is installed in a cylinder. For this reason, a valve seat is under high-temperature and high-pressure conditions, and there may be a problem of a nozzle becoming clogged with combustion byproducts, for example, carbon monoxide, soot, etc.
Conventional injection nozzles have a true-circular shape, and a fuel injection length that is relatively long. Furthermore, a fuel injection speed is comparatively low and fuel droplets are not completely vaporized, thus causing incomplete combustion, and causing combustion byproducts to be deposited, thereby resulting in blockage of the injection nozzle. Accordingly, fuel atomization efficiency is reduced, leading to incomplete combustion. As a result, problems such as air pollution and a reduction in the output of the engine are caused.
In an effort to overcome the problems of low combustion efficiency and air pollution, an injector having a conical nozzle hole which is increased in cross-sectional area in a direction in which fuel is injected was introduced in U.S. Pat. No. 5,353,992. However, in this structure, because of a low fuel injection speed, fuel atomization efficiency is still low. In addition, the problem of emission of noxious gas resulting from incomplete combustion, for example, carbon monoxide, is also not effectively mitigated.
Therefore, there is a need for a technique pertaining to an injector having a nozzle hole structure that can increase fuel injection speed and thus enhance fuel atomization efficiency.